Cooled ablation catheter devices and methods of use

ABSTRACT

Discloses herein are ablative catheters and methods of use. The catheters can include a cooling chamber for circulating cooling fluid within the catheter tip to reduce hot spots within the catheter tip and/or to reduce the formation of coagulum. A proximal cooling chamber can be positioned proximally to a thermal mass for cooling a proximal portion of the catheter. In addition, or alternatively, a distal cooling chamber can be positioned for cooling a distal portion of the catheter tip. The cooling fluid can flow the ablative catheter in an open, closed, or open and closed loop.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.12/247,619, filed on Oct. 8, 2008, now U.S. Pat. No. 9,023,030, whichclaims priority from the earlier filed U.S. Provisional Application No.60/978,511, filed Oct. 9, 2007, the entirety of which are herebyincorporated into this application.

BACKGROUND

Atrial fibrillation is a condition in the heart in which the generationof abnormal electrical signals causes irregular beatings of the heart. Aproven protocol for successfully treating this condition is open heartsurgery (sometimes referred to as the “maze” procedure) where severallong (i.e. approximately 2-10 cm) lesions are created in the endocardiumwithin the upper chambers of the heart (“atria”). These lesions blockthe flow of excess electrical impulses within the atria and allow theimpulse from the sinus node to properly regulate heart contraction.

However, because open heart surgery is highly invasive and requires alengthy patient recovery period, alternative methods for making lesionshave been recently explored. One such alternative is the use of ablationcatheters that includes one or more electrodes.

Typically, an ablation catheter is advanced into the heart via thepatient's vessels. When the electrodes are placed in the desiredposition within the heart chamber, radio frequency (“RF”) energy issupplied to the catheter thereby burning lesions into the endocardium.

Initial designs for ablation catheters generally comprised an elongatedshaft with an electrode mounted at the distal end. Either point andlinear lesions could be formed with these catheters by manipulating theplacement of the tip. However, because of the tendency for the tipelectrode to overheat and to lift off the tissue surface duringablation, creating suitable lesions using these catheters have beendifficult.

New catheter designs attempted to mitigate these disadvantages. Oneimprovement is the addition of a mechanism to cool the tip electrodeduring use to minimize the risk of embolism from overheated blood.Although these catheters mitigate some of the overheating problems,hotspots on the tip or in adjacent tissue may still develop.

Accordingly, while some conventional catheters are effective for cardiacablation, further advances could be beneficial.

SUMMARY OF THE INVENTION

Described herein are devices, systems and methods for medical treatmentand particularly for delivering ablative energy to target tissue whilereducing the formation of coagulum and/or for minimizing the effects ofbiological debris on the delivery of energy to tissue. In one aspect, anablation catheter having an ablative electrode tip is disclosed. Thecatheter can include a pathway or channel for delivery of cooling fluidto the ablative tip. Within the tip, cooling fluid can circulate in anopen loop, closed loop, and/or open/closed loop configuration.

In one embodiment, the catheter is sized and shaped for vascular accessand includes an elongate body extending between a proximal end and adistal end. The elongate body can include at least one inner fluid lumenand an electrode tip can be positioned proximate to the distal end ofthe catheter body. In one aspect, the tip includes an outer wall and aninner thermal mass having at least one fluid passageway therethrough. Acooling chamber, which is in fluid communication with the inner fluidlumen of the elongate body, can be positioned proximally to the thermalmass and adapted to cool a proximal portion of the electrode tipincluding the thermal mass.

In another aspect, the tip can further comprise multiple irrigationapertures in communication with the fluid passageway in the tip. Coolingfluid can flow into the proximal cooling chamber, through the thermalmass, and into the surrounding environment via the multiple irrigationapertures.

The cooling chamber, in one aspect, extends across substantially theentire width of the tip between the outer walls of the tip. The coolingchamber can be defined by a cavity at the proximate-most end of the tipthat is bounded at its distal end by the thermal mass and is bounded atits proximal end by a portion of the tip and/or by a portion of theelongate catheter body.

In another aspect, the size and shape of the cooling chamber is adaptedto cause fluid circulation within the cooling chamber. In one aspect,the cooling chamber has a greater cross-sectional area than the fluidinlet and/or outlet to the cooling chamber. In another aspect, a fluidingress to the cooling chamber is offset from a fluid egress from thecooling chamber.

In one aspect, the thermal mass comprises a material having a highthermal conductivity. A temperature sensor can be positioned at leastpartially within the thermal mass. In another aspect, the thermal massextends across substantially the full width of the tip with theexception of a cooling fluid flow path or flow paths extendingtherethrough. The cross-section of the fluid flow path or paths throughthe thermal mass can be less than the cross-sectional area of thecooling chamber. In one aspect, the size of the cooling chamber relativeto the fluid flow path or paths in the thermal mass results in anincrease in pressure and/or in fluid flow speed in the fluid flow pathor paths relative to the cooling chamber.

The electrode tip can include multiple irrigation apertures for thedelivery of cooling fluid to the environment surrounding the electrodetip. In one aspect, the irrigation apertures deliver fluid to the outer,distal surface of the tip. In another aspect, one or more of themultiple irrigation apertures is positioned distally of the temperaturesensor, thermal mass, and/or cooling chamber.

In another embodiment, the catheter described herein further comprises asecond cooling chamber positioned distally from the thermal mass.Cooling fluid can flow through the proximal cooling chamber, through thethermal mass, and then into the distal cooling chamber. In one aspect,irrigation apertures allow egress of the cooling fluid from the distalcooling chamber.

In one aspect, a cross-sectional width of the distal cooling chamber isgreater than the fluid flow path or paths through the thermal mass. Inanother aspect, the fluid passageway through the thermal mass is sizedand shaped to produce an increase in the fluid pressure within the fluidpassageway or passageways in the thermal mass with respect to theproximal and/or distal cooling chambers.

In another embodiment described herein a catheter device is disclosed.The catheter can be sized and shaped for vascular access and include anelongate body extending between a proximal end and a distal end andhaving at least one inner fluid lumen. An electrode tip positionproximate to the distal end of the catheter body can include an outerwall and an inner thermal mass having at least one fluid passagewaytherethrough. The tip can include a proximal cooling chamber in fluidcommunication with the inner fluid lumen of the elongate body andpositioned proximally of the thermal mass and adapted to cool a proximalsurface of the thermal mass, and a distal cooling chamber positioneddistally of the thermal mass. A fluid path can extend from the proximalcooling chamber, through the at least one fluid passageway in thethermal mass, and into the distal cooling chamber. Cooling fluid canthen exit the tip through multiple irrigation apertures in communicationwith the distal cooling chamber. The at least one passageway through thethermal mass can be sized and shaped to produce a pressure increasewithin the at least one fluid passageway with respect to the proximal ora distal cooling chamber.

In another embodiment of the catheter device described herein, anelectrode tip includes combined open and closed loop cooling flow paths.In one aspect, the elongate body include a second fluid lumen for theremoval of cooling fluid from the tip. For example, cooling fluid canflow through a first fluid lumen within the elongate body and into aproximal cooling chamber. After circulating through the proximal coolingchamber, at least a portion of the cooling fluid is then removed via thesecond fluid lumen. Cooling fluid not removed via the second fluid lumenflow can exit the tip via irrigation apertures. Thus, a portion of thefluid flows in a closed loop path (and is removed through the catheterbody) and a portion of the fluid flows into the environment surroundingthe distal tip in an open loop path. In one aspect, the open loop pathincludes a fluid pathway through a thermal mass and/or distal coolingchamber.

In one aspect, the open and closed loop flow paths are separate from oneanother. For example, cooling fluid can flow, via a first flow path,into a first cooling chamber, circulate therein, and then be removed.All of the cooling fluid can exit through the elongate body of thecatheter without exiting via irrigation apertures into the surroundingenvironment. In a separate, second flow path, fluid can be delivered tomultiple irrigation apertures and enter the environment surrounding theelectrode tip. In one aspect, fluid within the first and second flowpaths does not mix within the electrode tip.

Further described herein are methods of ablating tissue. One exemplarymethod includes the steps of providing a catheter having an electrodetip including an outer wall and an inner thermal mass having at leastone fluid passageway therethrough, a proximal cooling chamber positionedproximally of the thermal mass and adapted to cool a proximal surface ofthe thermal mass, and a distal cooling chamber positioned distally ofthe thermal mass. The method can include delivering fluid into theproximal cooling chamber, then moving the fluid through the thermal massand into the distal cooling chamber. In one aspect, fluid is thenreleased into the surrounding environment via multiple irrigationapertures in communication with the distal cooling chamber.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory onlyand are not restrictive of the invention, as claimed. In addition,structures and features described with respect to one embodiment cansimilarly be applied to other embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, provide illustrative embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a partially transparent view of one exemplary embodiment of anablation catheter described herein;

FIG. 2A is a longitudinal cross-sectional view of one embodiment of anelectrode tip described herein;

FIG. 2B is a transverse cross-sectional view of the electrode tip ofFIG. 2A;

FIG. 3 is a cross-sectional view of another embodiment of an electrodetip described herein;

FIG. 4 is a cross-sectional view of yet another embodiment of anelectrode tip described herein;

FIG. 5 is a cross-sectional view of still another embodiment of anelectrode tip described herein; and

FIG. 6 is a cross-sectional view of another embodiment of an electrodetip described herein.

DETAILED DESCRIPTION

Disclosed herein are cooled ablation catheters and methods of use. Ingeneral, the catheters include a flow path that provides cooling to adistal tip. The catheter can include an electrode tip having irrigationapertures for delivery of a cooling fluid to the environment surroundingthe distal tip and/or to the surface of the distal tip. In addition, theelectrode tip can comprise a proximal cooling chamber through whichcooling fluid circulates prior to egress through the irrigationapertures. The proximal cooling chamber can reduce hotspots sometimesassociated with conventional ablation catheters.

FIG. 1 provides a cut-away view of one exemplary embodiment of anablation catheter device 10 for use with the distal tip structuredescribed herein. Device 10 can include an elongate body 12 extendingbetween a proximal section 14 and a distal section 16. The distalsection includes an electrode tip 20 positioned to deliver ablativeenergy to tissue and is discussed in detail below.

In one aspect, the proximal portion of device 10 includes a handle 22for grasping by a user. The handle can incorporate a variety of featuresto facilitate control of the catheter and/or mating of the catheter witha source of fluid, a source of ablative energy, a temperature display,sensors, and/or control software/hardware. In one aspect, handle 22includes at least one fitting for mating with a source of cooling fluidand can include, two, three, or more than three ports 24 for receivingor expelling fluid. In addition, the catheter can include matingelements 26 for receiving and transmitting ablative energy to the distaltip. One skilled in the art will appreciate that a variety of catheterhandle configurations are contemplated depending on the features of thecatheter body 12, distal tip 20, and/or the intended use of device 10.

In another aspect, handle 22 can include a control mechanism 28 fordirecting movement of a distal portion of elongate body 12. Device 10can include an articulating section of catheter body 12 that iscontrolled via the proximal control mechanism. In one aspect, a distalportion of the catheter body can be deflected or bent. The articulationsection of the body can facilitate insertion of the catheter through abody lumen (e.g., vasculature) and/or placement of electrodes at atarget tissue location. The articulation section can provide one or moredegrees of freedom and permit up/down and/or left/right articulation.One skilled in the art will understand that the control mechanism andarticulating portion of the catheter can include the variety of featuresassociated with conventional articulating catheters.

Elongate body 12 can be defined by a flexible catheter body extendingbetween handle 22 and distal section 16. In one embodiment, body 12 canhouse at least one fluid passageway for the transfer of cooling fluid toand/or from tip 20. In addition, body 12 can house electrical conductors(e.g., wires) for transmitting sensed signals and/or ablation energy.Still further, articulation mechanisms, such as, for example, pull wirescan extend along body 12 to an articulation section of the device. Oneskilled in the art will appreciate that body 12 can represent thevariety of know catheter structures for travel through a body cavity,such as, for example, a vascular lumen.

The distal section 16 of device 10 can include a portion of the catheterbody and/or tip 20 comprising at least one electrode for deliveringablation energy, for sensing physiological signals, and/or for acting asa return electrode. In one aspect, multiple ring electrodes 30 arepositioned around the distal portion of the catheter. The ringelectrodes can permit sensing and/or mapping of cardiac signals. FIG. 1illustrates three ring electrodes 30 positioned proximally from distaltip electrode 20. Any of the ring electrodes and/or tip electrode can bepaired to sense physiological signals.

In addition to sensing, the distal portion of device 10 can deliveryablation energy in a bipolar and/or monopolar manner. For example, radiofrequency, microwave, and/or other ablative energy can be delivered viadistal tip 20. Ring electrode(s) 30 and/or a separate ground pad can actas a return electrode.

FIGS. 2A through 6 illustrate exemplary embodiments of distal tip 20. Inone aspect, tip 20 is defined at least in part by an electrode fordelivering ablative energy to target tissue. Tip 20 includes a flowpath, indicated by arrows 21, for cooling the tip. As cooling fluidmoves through tip 20, the fluid draws heat away from tip to control orreduce the temperature of the electrode. The reduced temperature caninhibit coagulum formation on device 10.

A build up of biological materials on the outer surface of the tipand/or in the area surrounding the tip can result in less effectiveenergy transfer to the tissue. This effect can be seen as a rise inimpedance and a corresponding increase in tissue heating and/or charringimmediately adjacent to the tip. Cooling of the tip can permit moreefficient energy transfer to tissue and allow larger lesion sizes for agive electrode mass or for a given amount of ablative energy transmittedto the tip.

In one aspect, the flow path directs cooling fluid through tip 20 to theouter surface of tip 20. Movement of fluid, such as cooling fluid,around tip 20 while the device is in contact with tissue, and energy isdelivered to the tissue, can inhibit impedance rise. The movement of thefluid sweeps biological material, such as, for example, blood andtissue, away from the tip to reduce a build-up of embolic material on oradjacent to the tip.

In another aspect, tip 20 further includes at least one cooling chamberconfigured for cooling hotspots associated with conventional ablationcatheters. While previous efforts to control the temperature of ablationcatheters and to reduce impedance rise have focused on the distal-mostouter surface of the catheter, other areas of the tip or electrode canalso exhibit unwanted temperature rise. In one aspect, a proximalcooling chamber is positioned within tip 20 for cooling. The coolingchamber can receive a flow of fluid to draw heat away from the proximalportion of the electrode, such as, for example, a portion of the tipadjacent to the catheter body where RF current tends to concentrate.

In one embodiment, tip 20 comprises a body 41 having a fluid passagetherethrough. Body 41 can be constructed of one or more segments thatare detachably or fixedly mated with one another and together define thefluid passageway. In one aspect, body 41 includes a sidewall 64 definingan outer surface 43. An insert or inserts can be mated therein to definethe fluid passageways. The tip can alternatively be constructed of asingle unibody structure in which fluid passageways, including coolingchambers, are formed. Regardless of its construction, body 41 can beformed of a variety of electrically and/or thermally conductivematerials including, for example, platinum, iridium, stainless steel,gold, plated brass, and combinations thereof.

FIGS. 2A and 2B illustrate one embodiment of tip 20 having a proximalend 40 and a distal end 42. The proximal portion of the tip can matewith a catheter body 12. In one aspect, proximal portion 40 includes anarea of reduced diameter or width for receipt within a portion of thecatheter body. An inner surface of the catheter body wall can surroundand mate with the outer surface of body 41 at the area of reduceddiameter. Alternatively, the tip and catheter body could mate in a butend connection, the tip could be positioned within a sidewall of thecatheter body, and/or the tip could extend around a portion of the outersurface of the catheter body. One skilled in the art will appreciatethat a variety of mating mechanism, including a frictional, mechanical,and/or adhesive engagement are considered.

The proximal portion of tip 20 can mate with various lumens, wires,and/or control mechanisms extending through body 12. In one aspect, afluid lumen 44 extends through proximal portion 40 of tip 20. The fluidlumen can be in fluid communication with a fluid lumen in catheter body12. In one aspect, a tubular body extends from body 12 into tip 20.Alternatively, the fluid lumen of tip 20 can be defined by a channelwith within tip 20, such as, for example, within reinforcing member 48.In another aspect, multiple fluid lumen can extend into and/or throughthe proximal portion 40 of tip 20.

Where the catheter includes an articulating region, control wires (e.g.,push/pull wires) can be mate with tip 20. In one aspect, the proximalportion 40 of the tip includes a reinforcing or anchor member 48positioned within tip 20. The reinforcing member can be defined by adistinct structure mated within outer wall 64 of the tip body 41.Alternatively, the tip and reinforcing member can have a unibodyconfiguration. In one exemplary aspect, reinforcing member 48 is definedby a stainless steel insert mated with the body 41 of tip 20. Controlwire 49 can mate with reinforcing member 48 to anchor the distal end ofthe control wire. However, such wires can alternatively, oradditionally, be fixed at a more proximal location of device 10.

In another aspect, electrically conductive wires can extend through theproximal portion of tip 20 to deliver energy and/or to permitcommunication with a sensor 46 positioned within tip 20. In one aspect,sensor 46 is a temperature sensor defined by, for example, athermocouple or thermistor.

The body 41 of tip 20 can further include a thermal or electrode mass 60positioned within tip 20 and a proximal cooling chamber 62. Coolingchamber 62 is positioned proximal to at least a portion of the thermalmass 60 and/or adjacent to the proximal portion of tip 20. As ablationenergy moves through tip 20, areas of increased current density candevelop and result in localized hotspots. The device 10 described hereincan reduce the effect of proximal hotspots through the use of a proximalcooling chamber. As cooling fluid moves through tip 20, the coolingchamber can represent an area of increased volume relative to a fluidpathway 50 through mass 60. Cooling fluid can circulate through thecooling chamber before exiting through fluid pathway 50 in mass 60. Asthe cooling fluid passes, it can absorb heat and reduce the effect oflocalized hotspots.

In one aspect, cooling chamber 62 extends across the majority of thewidth of the tip proximal to mass 60. In another aspect, the coolingchamber extends between sidewalls 64. Cooling fluid moving through thecooling chamber can draw heat from sidewalls 64 of tip 20, from mass 60(e.g., the proximal surface thereof), and/or from other portions of body41 of tip 20. Cooling fluid then moves through thermal mass 60 and fluidpathway 50. In one aspect, fluid ultimately flows in one direction,proximal to distal, through the cooling chamber. However, within thecooling chamber cooling fluid can circulate to absorb heat.

Mass 60 can define a portion of a cooling fluid flow path 50 between aproximal cooling chamber 62 and the point of egress of cooling fluidfrom tip 20. In one aspect, mass 60 is defined by electricallyconductive materials and/or thermally conductive materials, examples ofwhich include, brass, copper, stainless steel, and combinations thereof.In another aspect, mass 60 is defined by a thermally conductivematerial, but not necessarily an electrically conductive material.

As illustrated in FIGS. 2A and 2B, a temperature sensor 46 can bepositioned within mass 60. In one aspect, the thermal conductivity ofthe mass facilitates temperature sensing while sensor 46 is positionedwithin mass 60. For example, mass 60 can provide little or no thermalinsulation, such that the temperature of the outer surface of the tip issubstantially equal to the temperature of the sensor.

In one aspect, mass 60 is comprised of the same material as a sidewall64 of body 41 and/or is formed of unibody construction. Alternatively,all or a portion of mass 60 can be defined by a separate structure andcan mate with sidewall 64. The concept of a sidewall and mass 60 may bediscussed as separate elements for the sake of convenience and/orclarity, but such a description does not limit the tip, as describedand/or claimed, to a configuration in which the thermal mass is adistinct structure mated with the sidewall. In addition, the outersurface of the thermal mass can define a portion of the outer surface ofthe tip. For example, the sidewall can define the outer surface of thetip adjacent to a portion of a cooling chamber, while the outer surfaceof the thermal mass can define a different portion of the outer surfaceof the tip.

As mentioned above, mass 60 can include at least one fluid passageway 50therethrough. In one aspect, mass 60 is formed of generally fluidimpervious materials and the size and shape of fluid passageway(s) 50defines the flow rate of cooling fluid through tip 20. Thus, mass 60 canextend across substantially the whole width of tip with the exception ofa fluid pathway or pathways.

Heat transfer between tip 20 and fluid within the cooling chamber can beenhanced in several ways. In one aspect, the configuration of thecooling chamber and/or fluid inlet/outlet of the cooling chamber directsfluid circulation within the cooling chamber. For example, coolingchamber 62 can have a larger cross-section area than lumen 44 and/orfluid pathway 50. As fluid enters the cooling chamber, the increasedcross-section causes the fluid to circulate with the chamber beforeexiting. To enhance this effect, the fluid inlet and outlet of thecooling chamber can be offset from one another. As illustrated in FIG.2, fluid ingress 66 from lumen 44 is offset laterally or radially fromfluid egress 68 into fluid pathway 50. As a result, fluid tends tocirculate through the cooling chamber as it moves through the coolingchamber. Additional features such as, baffles (not illustrated), canalso or alternatively be placed with the cooling chamber and/or inadjacent fluid lumens. In yet another aspect, the fluid ingress and/oregress of chamber 62 can facilitate fluid circulation by directing thecooling fluid at an angle with respect to the longitudinal axis of tip20 and/or device 10. The angle of the inlet and/or outlet can directfluid in a swirling motion to increase heat transfer.

The fluid pressure profile of tip 20 can additionally or alternativelyassists with heat transfer. In one aspect, the relative size of thecooling chamber with respect to the fluid passageway through the thermalmass provides an increase in fluid pressure within fluid passageway 50.The cooling chamber can have a size (e.g., cross-sectional area) that islarger than the cross-sectional area of the fluid outlet from thecooling chamber and/or larger than the cross-sectional area of the fluidflow path 50 through the thermal mass. This size differential canincrease fluid pressure down stream of the cooling chamber. For example,the fluid pressure can be higher in the fluid passageway through thethermal mass compared to the fluid pressure in the proximal coolingchamber. The pressure differential can facilitate circulation of fluidwithin the cooling chamber and/or assist with heat transfer between thecooling fluid and the thermal mass.

Turning now to the distal portion 42 of tip 20, device 10 can includefluid egress for delivery cooling fluid to an area adjacent to the outersurface of the tip. In particular, device 10 can have an open-loopconfiguration in which cooling fluid exits the device through tip 20. Inone aspect, the distal portion of tip 20 include at least one irrigationaperture 54 for delivery cooling fluid to the tissue/tip interface. Forexample, FIG. 2B illustrates a cut-away view of tip 20 with fluidpassageway 50 extending to six irrigation apertures 54. In one aspect,fluid passageway 50 splits into multiple branches 50′ to connect to theirrigation apertures. However, multiple passageway 50 could connect tomultiple apertures 54 and/or branches 50′ could feed multiple apertures.The exact number of irrigation apertures and the size (i.e.,cross-sectional area/width) of the fluid passageway(s) 50 and branches50′ can be chosen based on the desired flow rate, flow pressure, anddistribution of cooling fluid.

In one embodiment, the fluid path branches 50′ and the irrigationapertures direct cooling flow in a direction substantially orthogonal toa longitudinal axis of the catheter body 12 and/or tip 20. In use, thecooling fluid can flow out of apertures 54 and swirl around tip 20 toreduce coagulation formation and/or to reduce blood concentrationadjacent to tip 20. In another aspect, fluid path branches 50′ and/orapertures 54 direct fluid flow at an angle in the range of about +/−30and 90 degrees, +/−45 and 90 degrees, or +/−60 and 90 degrees withrespect to the longitudinal axis of the catheter body and/or tip. Inanother aspect, fluid flow can be directed along a direction co-linearor co-axial to the longitudinal axis of the tip or catheter body. Inaddition, while coplanar fluid flow branches 50′ and apertures 54 areillustrated, a non-coplanar configuration is also contemplated.

In one aspect, irrigation apertures 54 are positioned such that as tip20 is moved into tissue, the apertures can be positioned below thetissue surface. For example, tip 20 can ablate tissue to a depth greaterthan the longitudinal spacing between the distal-most surface of the tipand the irrigation apertures. As cooling fluid exits the apertures, theadjacent tissue can direct cooling fluid around the outer surface of thetip to reduce the build-up of biological materials on the tip and/or todilute the concentration of biological materials in the fluidsurrounding the tip.

Irrigation apertures 54 and pathways 50′ can be formed in a variety ofways. In one aspect, channels are drilled through sidewall 64 and/ormass 60. While a macroporous tip 20 is illustrated in the Figures,microporous structures are also contemplated. For example, the sidewall64 and/or mass 60 could be formed from sintered material have a porositywhich allows cooling fluid flow therethrough. One skilled in the artwill appreciate that the variety of conventional macro and/ormicroporous catheter materials can be utilized to form tip 20.

FIG. 3 is a cross-sectional view of another embodiment of device 10where thermal mass 60 is spaced from the distal-most end of tip 20′. Inuse, spacing of the thermal mass can reduce heat transfer to adjacenttissue. A further reduction is heat transfer can be achieved with adistal cooling chamber 70. In one aspect, thermal mass 60 is spaced fromthe distal most end of tip 20′ and cooling chamber 70 is positionedtherebetween. Cooling fluid can flow through proximal cooling chamber62, through thermal mass 60, and into distal cooling chamber 70 beforeexiting irrigation holes within tip 20′.

In one aspect, the distal cooling chamber can extend across the fullwidth of body 41. For example, distal cooling chamber 70 can extendbetween the inner surfaces of sidewall 64. In addition, oralternatively, the distal cooling chamber can extend between thedistal-most surface of thermal mass 60 and the distal, inner surface ofsidewall 64. However, one skilled in the art will appreciate that thelength and width of distal cooling chamber 70 can vary depending on theintended use of device 20′, the amount of cooling fluid passedtherethrough, the desired temperature of the distal tip, and/or theamount of energy delivered via tip 20. In addition, baffles and/orpartitions can occupy a portion of the distal cooling chamber.

In one aspect, irrigation apertures 54 extend through the sidewall ofbody 41 proximate to distal cooling chamber 70. For example, coolingfluid can flow from the distal cooling chamber directly into irrigationapertures 54.

In one aspect, the distal cooling chamber can be adapted to circulatecooling fluid therethrough to increase heat transfer between an innersurface of tip 20 and the cooling fluid. In one aspect, the volume ofthe distal cooling chamber relative to the fluid passageway 50facilitates fluid circulation. The relatively smaller cross-sectionalarea of the fluid passageway through the thermal mass 60 (measured, forexample, at the outlet to the distal cooling chamber) compared with alarger cross-section and/volume of the distal cooling chamber provides apressure drop between fluid passageway 50 and distal cooling chamber 70.The pressure drop increases the speed of the fluid entering the distalcooling chamber and facilitate mixing and/or circulation within thedistal cooling chamber.

In addition, or alternatively, in the illustrated embodiment, the fluidinlet and outlet of the distal cooling chamber are not co-linear toencourage cooling fluid movement within the distal cooling chamber. Withrespect to FIG. 3, cooling fluid can enter the distal cooling chamberalong an axis parallel to the longitudinal axis of the tip and can exitthe distal cooling chamber via an orthogonal axis.

In one embodiment, the pressure profile of tip 20′ includes an increasein pressure in pathway 50 compared to both the proximal and distalcooling chambers. For example, the pressure in the fluid pathway (orpathways) through the thermal mass can be in the range of about 2 to 20times the pressure measured in the proximal and/or distal coolingchamber. In another aspect, the pressure in the fluid passageway 50 isabout 5 to 10 times greater than the pressure in the proximal and/ordistal cooling chamber. In yet another aspect, the pressure in the fluidpassageway through the thermal mass is in the range of about 40 and 60psi, while the pressure in the proximal chamber can be in the range ofabout 6 and 10 psi and the pressure in the distal cooling chamber can bein the range of about 4 and 6 psi. The higher pressure in the fluidpassageway(s) through the thermal mass can facilitate heat transfer inthe proximal and distal cooling chambers.

The pressure within the distal cooling chamber 70 can also, oralternatively, be chosen to select the desired exit speed of the coolingfluid from the irrigation apertures. In one aspect, the pressure in thedistal cooling chamber and the size, shape, and number of irrigationaperture can be selected to provide a fluid exit velocity from theirrigation apertures in the range of about 50 and 700 inches/second.

FIG. 4 illustrates another embodiment of the ablating catheter tip. Tip20″ includes a blunt distal end with fluid pathway(s) 50 positionedadjacent to a distal most outer surface 72 of the tip. Tip 20″ providesa reduce thermal mass 60 between the cooling fluid pathways and thedistal most end of the tip such that the temperature of the tissuecontact surface is reduced by the presence of cooling fluid and/orreduced thermal mass present at the distal-most end of the tip (ascompared, for example, to tip 20 of FIG. 2A). The size (lateral widthand/or longitudinal height) of the fluid pathway(s) adjacent to thedistal most surface, the number of fluid pathway branches 50′, and/orthe fluid flow rate can be variety to control heat transfer betweensurface 72 and tissue. One skilled in the art will appreciate that theshape of the distal-most portion of the catheter 20 can be variedaccording to the use of device 10 and the tip described with respect toFIG. 4 is one exemplary embodiment that can be substituted for thedistal-most portion of the other catheter tips described herein.

FIGS. 5 and 6 illustrate yet another embodiment of an ablation cathetertip described herein. Generally, the catheter tips 20, 20′, 20″described above have an open loop configuration where fluid flows fromthe catheter body 12 through the tip and out through irrigationapertures. Conversely, the tip of FIGS. 5 and 6 includes a lumen for thewithdrawal of at least a portion of the cooling fluid from the tip. Theclosed loop or partially closed loop flow path eliminates or reduces thedelivery of cooling fluid to the exterior surface of the electrode tip.For example, with respect to FIG. 5, first and second fluid lumens 44 a,44 b are in fluid communication with tip 20′″. Lumen 44 a can deliver acooling fluid into, for example, proximal cooling chamber 62. At least aportion of the cooling fluid can then continue on a path as describedwith respect to FIGS. 2A through 4 above. However, tip 20′″ includes asecond fluid lumen 44 b for removing cooling fluid after the coolingfluid has absorbed heat within the proximal cooling chamber. The secondfluid lumen can return the heated fluid to catheter body 12 for egressfrom device 10 through a proximal location (e.g., handle 22). As aresult, heat is removed from tip 20′″ through more than one coolingfluid flow path.

Partially closed-loop cooling allows the fluid flow rate into tip 20′″to exceed the fluid flow rate exiting irrigation apertures 54.Accordingly, the amount of fluid circulating through proximal coolingchamber 62 can be increased without requiring a corresponding increasein the fluid flow rate into a patient. Since it is generally preferredto avoid excessive saline delivery during cardiac ablation, the use ofboth open and closed loop cooling flow paths can allow increased coolingwithout a corresponding increase in cooling fluid delivered into apatient.

While no distal cooling chamber is illustrated in FIG. 5, a closed loopor partially closed loop cooling flow path could similarly oralternatively withdraw cooling fluid from a distal cooling chamber. Inone such exemplary embodiment, second fluid lumen 44 b could extend to adistal cooling chamber.

In another embodiment, the electrode tip can include both opening loopcooling and fully closed loop cooling. FIG. 6 illustrates one exemplaryembodiment of tip 20″″ having two separate fluid flow paths. The first,path 76 is a closed loop flow path that delivers fluid to and withdrawsfluid from a cooling chamber, such as, for example, cooling chamber 62.First fluid path 76 can include first and second fluid lumens 44 a, 44 bextending through catheter body 12 and into tip 20″″. The cooling fluidenters cooling chamber 62, circulates therein, and absorbs heat. Thecooling fluid is then withdrawn through lumen 44 b and can exit thecatheter.

Fluid path 78, conversely, is an open loop fluid flow path in which thecooling fluid travels through catheter 12 and is delivered to theexterior of tip 20″″. In one aspect, flow path 78 includes a lumen 44 cextending between the proximal portion of tip 20″″ and irrigationapertures 54. In one aspect, flow path 78 provides minimal impact oncooling of the tip as fluid travels through path 78 through the tip.Instead, the fluid of flow path 78 provides reduced coagulationformation on the outer surface of the tip.

Alternatively, flow path 78 can extend through mass 60 and flow througha distal cooling chamber (not illustrated) prior to exiting tip 20″″.For example, tip 20″″ could include a distal chamber similar to distalcooling chamber 70 into which cooling fluid flows prior to exiting theablation catheter.

Regardless of the configuration of the open and closed loop flow path,the presence of two separate flow paths can allow independent control offlow rates and/or cooling fluid pressures. For example, the closed loopfluid pressure could be higher than the open loop fluid pressure in tip20″″. In addition, different cooling fluids can be used in the differentflow paths.

Other embodiments of the invention will be apparent to those skilled inthe art from consideration of the specification and practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with a true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A catheter device, comprising: a catheter sizedand shaped for vascular access and including an elongate body extendingbetween a proximal end and a distal end; an electrode tip positionedproximate to the distal end of the elongate body, the electrode tipincluding an outer wall having an outer surface and an inner surface, anelectrode mass positioned within the outer wall to define a proximalcooling chamber and a distal cooling chamber, the proximal coolingchamber extending between the inner surface of the outer wall from thedistal end of the elongate body to a proximal-most surface of theelectrode mass, the distal cooling chamber extending from a distal-mostsurface of the electrode mass to a distal inner surface of the outerwall, the electrode mass including a fluid pathway extending from itsproximal-most surface to its distal-most surface to define a fluidoutlet from the proximal cooling chamber and a fluid inlet to the distalcooling chamber, wherein a circumference of the fluid pathway is whollybounded by the electrode mass, the electrode tip further comprising oneor more irrigation apertures extending through the outer wall proximatethe distal cooling chamber, a fluid lumen extending within the elongatebody and terminating proximate a proximal-most portion of the proximalcooling chamber to define a fluid inlet to the proximal cooling chamber,wherein the fluid inlet to the proximal cooling chamber and the fluidoutlet from the proximal cooling chamber are laterally offset from oneanother.
 2. The device of claim 1, wherein the electrode mass is athermal mass including a material having a high thermal conductivity. 3.The device of claim 1, wherein a temperature sensor is positioned atleast partially within the electrode mass.
 4. The device of claim 3,wherein the one or more irrigation apertures include multiple irrigationapertures.
 5. The device of claim 4, wherein at least one of themultiple irrigation apertures is positioned distally of the temperaturesensor.
 6. The device of claim 4, wherein at least some of the multipleirrigation apertures are positioned distally with respect to the distalcooling chamber.
 7. The device of claim 1, wherein the fluid pathwaythrough the electrode mass is sized and shaped to produce an increase influid pressure within the fluid passageway through the physical barrierwith respect to the distal cooling chamber.
 8. The device of claim 1,wherein the outer wall of the electrode and the electrode mass arecomprised of different materials.